This invention constitutes an improvement over U.S. Pat. No. 4,462,700 granted to G. L. Agrawal on Jul. 31, 1984 entitled "Hydrodynamic Fluid Film Thrust Bearing" and commonly assigned to United Technologies Corporation. As is well known in this technology, the thrust bearing consists of a plurality of the top foil plate segments and a plurality of segmented bump foils configured in wedge shape or pads. The top foil plate segments fit over the segmented bump foils and each of the segments are attached to the upper face of the foil plate. Hence, the number of top foil plate segments is identical to the number of the bump foil segments. The leading edge of the segments, i.e. the top foil plates and the bump foils, are individually welded to the foil plate and are uniformly spaced around the circumference of the foil plate. The trailing edge is unattached and left free to move axially. The foil plate is a toroidally shaped disk or washer like member and the inner diameter fits over the rotating shaft of the rotating machinery. The thrust bearing is sandwiched between the thrust runner and the thrust plate.
In this heretofore known thrust bearing design, each of the segments are welded to the foil plate and hence in a design that utilizes 7 pads of the bump foils and 7 pads of the top foil there are 14 leading edges that are welded to the foil plate. This number of welds inherently produces an undesirable warpage to the thrust bearing which adversely affects the load carrying capacity of the bearing. Additionally, it is customary to coat the top surface of each of the top foil pads with a dry film lubricated coating to reduce friction during the rotating machine start-up and coastdown, inasmuch as this surface comes into contact with the thrust runner since the rotational speed is not sufficient to maintain an air film. Since each top foil pad is coated it has been found that the thickness and texture of the coating on each of the pads tends to vary and is not uniform.
I have found that I can improve these types of hydrodynamic foil bearings by fabricating the top foil into a single piece that is relatively flat disk shaped similarly to the foil plate and is stamped into wedge shaped arcuate segments by a radial depression to define the top foils. The disk fits over the bump foils that are welded to the foil plate and the top foils stamped into the disk overlie the bump foils. The flat disk, which is a one piece configuration, eliminates the welding requirement and the entire top surface is coated, thus eliminating the necessity of coating individual pads. This results in a more uniform thickness and texture of the dry lubricant coating.